Dovetails for positive retention in an over-molded actuator

ABSTRACT

Positive retention features are provided on an actuator of a magnetic disk drive thereby increasing the structural rigidity of the actuator in attachment of a voice coil to the actuator. The positive retention features are defined by a plurality of protrusions having compound curved shapes including reverse or inward facing edges. The natural tendency of thermoplastic resin to shrink during cooling is used to an advantage in enhancing the rigidity of the connection between the voice coil and actuator body. The compound curved shapes of the positive retention features allows shrinkage of the thermoplastic resin in multiple directions around the features thereby maintaining desired actuator stiffness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/407,977, filed on Apr. 3, 2003, now U.S. Pat. No. 7,042,681 entitled“DOVETAILS FOR POSITIVE RETENTION IN AN OVER-MOLDED ACTUATOR”, whichclaims priority from U.S. Provisional Patent Application Ser. No.60/371,226, filed on Apr. 8, 2002, entitled “DOVETAILS FOR POSITIVERETENTION IN AN OVER-MOLDED ACTUATOR”, the disclosures of which areincorporated herein by their reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an actuator used in a magnetic diskdrive, and more particularly, to an actuator incorporating positiveretention features for enhancing the attachment voice coil to theactuator which allows for a superior servo system capable of achievinghigher drive capacities.

BACKGROUND OF THE INVENTION

Rotary type actuators are commonly used for positioning magneticread/write heads on recording tracks of a magnetic disk. Exactpositioning of the actuator to ensure proper tracking of the magneticread/write heads is of paramount concern in producing a quality diskdrive. As track densities increase, the construction of the actuatormust be capable of providing consistent and reliable positioning. Inmany disk drive systems, the construction of an actuator assembly mayinclude multiple actuator arms and multiple suspensions which positioncorresponding multiple read/write heads on a disk pack having multiplemagnetic disks. Because of the increased size of such an actuatorassembly, one continuing concern in the design of such an assembly arethe vibrational characteristics of the actuator assembly. The actuatorassembly should be of a design that limits undesirable actuatorvibration. Providing the requisite stiffness in an actuator assembly isoften difficult because of a number of design limitations to include theinability to integrally mold or extrude each component of the actuator.For example, a voice coil must be attached to the actuator assembly,typically by an over-molded thermoplastic resin. Because the resin andvoice coil cannot be integrally molded or extruded with the body of theactuator assembly, complex vibrational variables are introduced inoperation of the actuator assembly. Thus, one inherent problem in use ofany type of thermoplastic resin to attach the voice coil is that thethermoplastic resin itself has a lower modulus than the metallicactuator assembly thereby reducing actuator stiffness.

Another inherent problem in use of any type of thermoplastic resin usedto join a voice coil and actuator is that thermoplastic resin willshrink in size as the molten plastic cools after molding. In mostcircumstances, the over-molded resin has a tendency to shrink in adirection away from the voice coil thereby creating voids or thinnedsections of thermoplastic resin around the voice coil. As wellunderstood by those skilled in the art, thermoplastic resin itself doesnot have good adhesion characteristics with respect to adhering to theactuator; rather, the over-molded resin acts as a mechanical connectionfor joining the voice coil to the actuator. Therefore, gaps or voids inthe thermoplastic resin due to shrinkage reduce the ability of thethermoplastic resin to provide a stiff connection.

FIG. 1 illustrates one prior art approach in securing a voice coil tothe actuator. The method shown in this figure is described in the U.S.Pat. No. 5,122,703 and is illustrated at FIG. 6(A) thereof. In thisapproach, the actuator arm 100 has a single dovetail 102 located behindthe bearing of the actuator and an over-molded thermoplastic resin 106circumferentially encapsulates the outside diameter of the voice coil104 with remaining portions of the over-molded resin 106 forming aborder that encapsulates the dovetail 102. The sole joint created by thelone dovetail behind the bearing of the actuator is not a robust designand allows the voice coil and over-molded resin to displace from thedovetail 102 in micro-movements about the joint thereby resulting in aloss of stiffness. The relatively thin border of plastic resin along theoutside diameter of the voice coil does not provide the requiredstructural support to ensure the voice coil is sufficiently integratedinto the actuator.

FIG. 2 illustrates another prior art approach wherein actuator 110includes two integral yoke arms 112 which extend away from the proximalor rear portion of the actuator body. An over-molded resin 116 thenencapsulates both of the yoke arms as well as the voice coil 114. Theintegral yoke arms increase overall stiffness as compared to the priorart approach of FIG. 1; however, by totally encapsulating the yoke arms,the thermoplastic resin shrinks in all directions towards the yoke arms.Accordingly, the resin is drawn away from the outside diameter of thecoil creating gaps between the plastic and the outside diameter of thecoil. These gaps reduce the overall actuator stiffness

FIG. 3 illustrates another example of a prior art approach in which anactuator 120 includes a pair of yoke arms 122, and a voice coil 124 issimply glued to the corresponding inner surfaces of the yoke arms. Whilethe glue may provide good contact between the yoke arms and the coil,the glue may become soft at upper ranges of disk drive operatingtemperatures. The softening glue reduces stiffness of the actuator byallowing micro movements of the voice coil.

Another prior art approach as shown in FIG. 4 is to provide an actuator128 with a plurality of teeth or curved protrusions on the innersurfaces of the yoke arms 130. These protrusions break up the normallysmooth inner surface of the yoke arms thereby providing a greatersurface area for the thermoplastic resin (not shown) to attach. However,even with the curved protrusions/teeth, a problem still exists inshrinkage of the plastic resin in a direction away from the yoke armsthereby reducing overall stiffness of the actuator.

Yet another prior art approach for attachment of a voice coil to anactuator is shown in the actuator 136 of FIG. 5. This approach requiresthe drilling of holes 140 in the yoke arms 138. The thermoplastic resin(not shown) fills the holes 140 thereby providing a locking feature tosecure the voice coil (not shown). One distinct disadvantage in thisapproach is that the holes drilled in the yoke arms require a separatedrilling operation which thereby increases the complexity ofmanufacturing, as well as potentially introducing contamination in adisk drive by small burrs or debris which may not be properly cleanedfrom the actuator prior to assembly of the disk drive.

One object of the present invention is to provide positive locking orpositive retention features on the back end structure of an actuatorwhich allows attachment of the voice coil without sacrificing ordegrading stiffness of the actuator assembly. Another object of thepresent invention is to provide an actuator which may incorporatepositive locking features at a minimum cost. Yet another object of thepresent invention is to provide a means to attach the voice coil bythermoplastic resin which takes advantage of the resin's naturaltendency to shrink upon cooling.

SUMMARY OF THE INVENTION

In accordance with the present invention, an actuator assembly isprovided which incorporates positive locking protrusions or positiveretention features for attaching the voice coil to the actuator. In apreferred embodiment of the present invention, an actuator body isprovided which may be manufactured in an extrusion process. The actuatorbody includes a pair of yoke arms extending from the back end or rearportion of the actuator body. Each of the yoke arms has a plurality ofpositive locking or positive retention features which enhance athermoplastic resin's ability to join the yoke arms to a voice coil.Through a molding operation, the resin encapsulates the outer edges ordiameter of the voice coil and inner surfaces of the yoke arms. Thepositive retention features are spaced along the inner surfaces of theyoke arms and incorporate protrusions having compound curved shapes. Oneof the curved areas on the features is a reverse or inward facing edge.Because the over-molded resin has a tendency to tightly shrink aroundthe positive retention features of compound curved shapes, shrinkagetherefore occurs in multiple directions. Structural rigidity andstrength of the connection is therefore enhanced between the yoke armsand the over molded resin.

The positive retention features/protrusions extend away from the innersurfaces of the yoke arms toward a central gap where the voice coil ispositioned. The positive retention protrusions each preferably include aneck portion and an enlarged end or head portion. The enlarged endportions have a curved shape which resembles a dovetail. The outer edgeof each of the positive retention protrusions can be separatelyidentified as including an outward facing edge section and a pair ofreverse/inward facing edge sections. One way to conceptually define thereverse/inward facing edge sections is to describe them as being thosepoints along the outer edges of the protrusions which generally facetowards the inner surfaces of the yoke arms. Alternatively, the reversefacing edge sections can be defined as points along the outer edges ofthe positive retention features wherein a line drawn normal to eachpoint results in the line intersecting with the inner surfaces of theyoke arm. The outward facing edge sections generally face away from theinner surfaces of the yoke arms and toward the central gap where thevoice coil is positioned. These outward facing sections may be definedas those points along the outer edges of the protrusions wherein a linedrawn normal to each point results in the line not intersecting theinner surfaces of the yoke arms.

One particular advantage of the present invention is that the positiveretention or positive locking features may be extruded with the actuatorbody and therefore need not be separately attached or constructed.Accordingly, the manufacturing process for making the actuator issimplified thus reducing costs. As mentioned above with respect to theprior art approach of drilling holes in the yoke arms, creating positiveretention features by drilling raises manufacturing costs as well asintroducing contamination issues.

When the over-molded resin begins to cool after the molding process hasallowed the resin to flow between the voice coil and actuator body, theresin will shrink in the multiple directions surrounding the positiveretention features thereby providing a mechanically strong and stiffconnection. The areas of resin surrounding the reverse facing edgesections particularly enhance the stiffness of the connection becausethe resin is shrinking in a direction that causes the resin structure asa whole to remain locked against the positive retention features whichthemselves are integrally formed with the actuator body.

Other features and advantages of the present invention will becomeapparent from review of the following detailed description taken inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1–5 illustrate various prior art approaches in attachment of avoice coil to an actuator;

FIG. 6 is a perspective view of an actuator body which incorporates thepositive retention features of the present invention;

FIG. 7 is a fragmentary enlarged plan view illustrating the positiveretention features on corresponding yoke arms of the actuator body;

FIG. 8 is another fragmentary plan view further illustrating a voicecoil attached to the actuator body by an over-molded resin;

FIG. 9 is a cross-sectional view taken along line 9—9 of FIG. 8 showinghow the over-molded resin flows around the positive retention features;

FIG. 10 is a greatly enlarged plan view of a representative positiveretention feature; and

FIG. 11 is another greatly enlarged plan view of a pair ofrepresentative positive retention features, such as those identified inFIG. 7, illustrating the manner in which the over-molded resin shrinksaround the positive retention features thereby providing a mechanicallystrong and stiff connection.

DETAILED DESCRIPTION

FIG. 6 illustrates the positive retention features of the presentinvention incorporated within a standard actuator body 10. The actuatorbody 10 includes an integrally extruded base 12, actuator arms 14, andyoke arms 20. As well understood by those skilled in the art, a completeactuator assembly would further include a suspension (not shown) foreach arm 14, a slider (not shown) mounted to each suspension, and one ormore read/write heads (not shown) mounted to each slider. Each of theactuator arms 14 of the type shown in FIG. 6 include an opening 18 whichmay receive a corresponding swage plate (not shown) for connection ofthe actuator arms to their respective suspensions. A central bore hole16 is formed in the base 12, and the actuator body 10 rotates about abearing (not shown) which is mounted within the bore hole 16. The pairof yoke arms 20 extend angularly away from the base 12 and may befurther defined as including respective base sections 22 which attach tothe base 12, and respective arm sections 23 which extend away from thebase 12. A continuous web 24 may interconnect the base sections 22. Thepositive retention features 26 are mounted on the inner surfaces of therespective yoke arms. The positive retention features may be spacedalong the inner surfaces of the yoke arms, and may be sized to providean optimal interface for interconnection of the over molded resin.

While a particular type of actuator body is illustrated, it shall beunderstood that the positive retention features of the present inventionmay be incorporated within any number of different type of actuatordesigns which at least include a pair of yoke arms positioned at theback end or rear part of the actuator body.

Referring also now to FIGS. 7–10, the positive retention features 26 maybe further defined as including a neck area or portion 30 and anenlarged end portion 32 which extends from the neck 30. The edges of thepositive retention features 26 may be defined in separate sections toinclude a pair of reverse/inward facing edges 34 and an outward facingedge 36 interconnecting the pair of inward facing edges. The edges 34may be defined as those points along these edges which allow a line 38to intersect the inner surface 42 of the yoke arms when the line 38 isdrawn normal to the points. The significance of these inward facingsections 34 are discussed below with respect to the manner in which theover-molded resin shrinks around the positive retention features 26. Theoutward facing edges 36 would be those points along this edge whichallow a line 44 to be drawn normal to these points without intersectingthe inner surfaces 42.

Referring specifically to FIGS. 8 and 9, the over-molded resin 46 isshown which interconnects the actuator body to the voice coil 48. Theparticular pattern shown for the resin 46 simply represents one way inwhich to secure the voice coil and to provide for mounting of othercomponents to the actuator. Therefore, the present invention should notbe considered limited by the particular manner in which the over-moldedresin arranges with respect to the voice coil. In an injection moldingprocess during assembly of the actuator, the resin flows to fill thegaps or voids between the voice coil and the actuator. The voice coil iscentrally located between the yoke arms and is at least partiallyencapsulated within the resin around its outer diameter. Preferably, theyoke arms extend to a length which results in the voice coil havingapproximately 270° of the outer diameter bounded by the yoke arms andthe web interconnecting the yoke arms. As shown in FIG. 9, it ispreferable to have the over molded resin completely encapsulate thefeatures 26.

Referring to FIG. 11, the directional arrows indicate the manner inwhich the thermoplastic resin will shrink around the positive retentionfeatures. For clarity, the directional arrows are only shown around onepositive retention feature. Because of the multi-directional shrinkageof the resin around the positive retention features, strength of theconnection between the voice coil and actuator is increased becausemechanical locking of the resin to the positive retention features isnot structurally weak along any particular axis or direction. In otherwords, the shapes of the positive retention features which facilitatethe multi-directional shrinkage of the resin around the features ensuresthere is not a particular area or section along the yoke arms which doesnot have a positive locking arrangement with the resin. Thus, anyinduced stresses or bending moments placed upon the actuator in aparticular direction will allow the actuator to resist micro-movement ofthe voice coil since there are multiple locking structures havingstrength in many directions. Furthermore, the shrinkage of the resinaround the positive retention features in the manner shown in FIG. 11also limits the amount of resin which will be pulled away from the voicecoil as the resin shrinks towards the actuator. As shown in FIG. 11, thethermoplastic resin which flows between the positive retention featuresmay also be defined as forming a plurality of interlocking resinfeatures which fill the spaces between the plurality of positiveretention features. Accordingly, FIG. 11 also may described asillustrating a plurality of interlocking resin features in which eachinclude a neck portion 60 and an enlarged end or head portion 62.Accordingly, the positive retention features and the plurality ofinterlocking resin features form a combination of structural componentswhich increase stiffness, and thereby inhibit micro-movement of thevoice coil with respect to the actuator despite potential multiplestresses or bending moments which may be placed upon the actuator.

From the figures it can be seen that the positive retention features 26do not necessarily have to be of identical shape, and the particularshape of each of the retention features may be modified as necessary toprovide the desired level of interface with the over-molded resin.Although no positive retention features 26 are illustrated at the web24, it is also possible to place one or more positive retention features26 along this area as well.

By the foregoing invention, positive retention of the over-molded resinto the actuator body is achieved in a manner which maintains structuralintegrity as well as to utilize the inherent shrinkage properties ofplastic in favor of enhancing structural rigidity of the actuator.Because improved stiffness is achieved with the attachment of the voicecoil to the actuator, the disk drive may achieve higher drive capacity.

The particular design of the positive retention features allows thefeatures to be integrally extruded with the actuator body therebyeliminating the need for additional processing steps to incorporate thepositive retention features.

The yoke arms which extend approximately 270° around the voice coildiameter thereby constrain the voice coil in a more superior manner thanthe single dovetail approach in the prior art discussed above.

Since thermoplastic resin does not have any appreciable adhesioncapability and relies primarily upon mechanical locking, the reversefacing edges on the positive retention features thereby use themechanical locking capability of the plastic as means to enhanceinterconnection between the voice coil and the actuator.

By extruding the positive retention features within the same structureas the actuator body, the positive retention features may beincorporated in a more cost effective manner, as well as reducingcontamination issues which may occur with drilled holes in the actuatorbody.

The foregoing invention has been described in reference to a particularembodiment thereof; however, various other changes and modifications maybe made within the spirit and scope of the invention.

1. An actuator body comprising: an actuator base having a bore holeprovided therethrough; at least one actuator arm attached to said base;a pair of yoke arms extending angularly away from the actuator base; aplurality of protrusions integrally formed with each said pair of yokearms and extending away from inner surfaces of each said yoke arms, saidprotrusions each having a reverse facing edge; a voice coil; and anover-molded section interconnecting said voice coil to said yoke arms,said over-molded section being made of a thermoplastic resin whichshrinks around said protrusions to include shrinkage in a directiontoward said reverse facing edges of said protrusions and away from saidyoke arms.
 2. An actuator body, as claimed in claim 1, wherein: each ofsaid plurality of protrusions further include an enlarged end portionand a neck portion interconnecting said enlarged end portion to acorresponding inner surface of one yoke arm of said pair of yoke arms.3. An actuator body comprising: an actuator base having a bore holeprovided therethrough; at least one actuator arm attached to said base;a pair of yoke arms extending angularly away from the actuator base; aplurality of means integral with and extending away from inner surfacesof each of the yoke arms for positively retaining an over molded resinsection, said means for positively retaining having a plurality ofreverse facing edges; a voice coil; and said over molded sectioninterconnecting said voice coil to said yoke arms, said over-moldedsection being made of a thermoplastic resin which shrinks around saidmeans for positively retaining in a direction toward said reverse facingedges.
 4. An actuator body, as claimed in claim 3, wherein: said meansfor positively retaining includes a plurality of positive retentionfeatures spaced along inner surfaces of said pair of yoke arms, and saidplurality of reverse facing edges being disposed along said positiveretention features.
 5. An actuator body, as claimed in claim 4, wherein:said plurality of positive retention features each include an enlargedend portion and a neck portion interconnecting said enlarged end portionto a corresponding inner surface of one yoke arm of said pair of yokearms.